function [x sign] = signal4(step)
%SIGNAL4 y = sin(x) x[-2*pi 2*pi]
x = -3*pi:step:3*pi;
sign = zeros(1,length(x));
for k = 1:length(x)
    if (x(k) >= -2*pi) && (x(k)<=2*pi)
        sign(k) = sin(x(k));
    else sign(k) = 0;
    end;
end;